Navigation devices that include GPS (Global Positioning System) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems.
In general terms, a modern navigation device may comprise a processor, memory (at least one of volatile and non-volatile, and commonly both), and map data stored within said memory. The processor and memory usually cooperate to provide an execution environment in which a software operating system may be established, and additionally it is commonplace for one or more additional software programs to be provided to enable the functionality of the navigation device to be controlled, and to provide various other functions.
Typically these devices further comprise one or more input interfaces that allow a user to interact with and control the device, and one or more output interfaces by means of which information may be relayed to the user. Illustrative examples of output interfaces include a visual display and a speaker for audible output. Illustrative examples of input interfaces include one or more physical buttons to control on/off operation or other features of the device (which buttons need not necessarily be on the device itself but could be on a steering wheel if the device is built into a vehicle), and a microphone for detecting user speech. In one arrangement the output interface display may be configured as a touch sensitive display (by means of a touch sensitive overlay or otherwise) to additionally provide an input interface by means of which a user can operate the device by touch.
Devices of this type will also often include one or more physical connector interfaces by means of which power and optionally data signals can be transmitted to and received from the device, and optionally one or more wireless transmitters/receivers to allow communication over cellular telecommunications and other signal and data networks, for example Wi-Fi, Wi-Max GSM and the like.
Navigation devices of this type also usually include a GPS antenna by means of which satellite-broadcast signals, including location data, can be received and subsequently processed to determine a current location of the device.
The navigation device may also include or be configured to communicate with angular or linear accelerometers which produce signals that can be processed to determine the current angular and linear acceleration, and in turn, and in conjunction with location information derived from the GPS signal, velocity and relative displacement of the device and thus the vehicle in which it is mounted. Typically such features are most commonly provided in in-vehicle navigation systems, but may also be provided in navigation devices if it is expedient to do so. Accelerometer data may be stored and used to determine whether any exceptional driving events (for example, harsh braking or acceleration, swerving or other emergency manoeuvres) have occurred during a period of time.
Accelerometers may also be included in black box devices for vehicles, which do not provide navigation functions but log location, speed, acceleration and other vehicle data for transmission to a central server. Such devices are often included in commercial vehicles such as lorries, buses and taxis for monitoring purposes.
The position of installation of a navigation device, or other telematic device inside a vehicle is important, as internal antennas of the device are directly influenced by the position. For example a GPS antenna should have a clear view to the sky, and if it is located on one side of the device, that side should be the “upper side” when it is installed.
Furthermore, it is necessary to know the orientation of an accelerometer accurately in order to correctly process acceleration data from the accelerometer, and to correctly detect driving events such as curve driving or harsh braking or acceleration. Another problem is that accelerometers are often susceptible to temperature fluctuations, resulting in changes of measured acceleration data.
In known systems the installation position and orientation of a telematic device with respect to a vehicle is usually unknown, and the bearing and orientation of the vehicle with respect to the ground is unknown and frequently changes.
At present the installation position of a telematic and/or accelerometer device is determined by manual calibration, for example by manually pressing a button when the device is being installed and fixed to the car by the installer. At the time of calibration all relevant environmental conditions are known and can be used to calibrate the device correctly. Such calibrations are also usually performed on level ground, and the output of the accelerometer device can thus be calibrated.
Manual calibrations are time-consuming and subsequent variations in environmental conditions (for example, seasonal or daily variations in temperature) can subsequently cause inaccuracies. Furthermore, if the initial calibration is carried out inaccurately or if the orientation of a device changes after installation, there may be persistent, systematic inaccuracies in operation of the device.